Metal casting art



J- H. KEATING METAL CASTI-NG ART June 1, 1965 2 Sheets-Sheet 1 FiledOct. 19, 1961 INVENTOR. JOHN H. KEATING mTm ibkk ATTORNEYS June 1, 1965H. KEATING 3,186,678

METAL CASTING ART Filed bot. 19. 1961 2 Sheets-Sheet 2 FIG. 4

IN V EN TOR.

JOHN H. KEATING BY wsmmmljfimuz ATTORNEYS United States Patent 3,186,678IVETAL CASTING ART John H. Keating, Cleveland, Ohio, assignor to MonarchAluminum Mfg. (30., Cleveland, Ohio, a corporation of ()hio Filed Get.19, 1961, Ser. No. 146,183 6 Ciainis. ((11. 249-416) By prior artpractice it is usual to utilize a permanent or die casting mold, to themold cavity surfaces of which is applied a coating or mold release agentadapted to further production of a better product surface, especially byfurthering venting of the cast metal or a ready release of the castobject from the mold and to permit the use of iron or steel dies andmolds which otherwise would be severely and unacceptably eroded bymolten metal, especially aluminum. However, in a relatively short time,not unusually, for example, one shift or Working day, it has been foundnecessary that molds be scoured of the coating by sandblasting or thelike, and the coating replaced.

Such prior practice involves economic loss not only in the operations ofremoving and replacing the mold coatin" and in the resulting down-timeof the mold; but also from the fact that the repeated scouring orcleaning operations change the mold cavity surfaces to an extentefiectively destroying the mold in consequence of changed dimensions orconfiguration of the ultimate product.

By the present invention there is provided in a mold of the characterdescribed a novel coating advantageously obviating many untowardfeatures to be ascribed to the prior art mold coatings. Moreparticularly at least the cavity, i.e., the article forming surfaces ofthe mold, is provided with a plated porous hard chromium surface. Thishas been found first to eliminate the need for the prior used coatingsof the type previously described and consequently the subsequent usualscouring and recoating operations along with the detrimental physicaland economic results hitherto arising.

Also a product is obtained by this invention having, throughout the lifeof the plating, a surface consistently better reproducing the moldcavity surface. This of course substantiallyeliminates grinding, orother operations on the product previously required in consequence ofvariations of successive objects from intended form. The finishresembles that 011 die castings of much lower melting point alloys. Itis generally possible better to cast a desired surface finish intheobject; whether a smooth surface or one having particulardecorativecontours or configurations formed in the mold cavity; The castsurfaces produced by this invention also generally have a finer grainstructure, therefore resulting in more reflective surfaces and alsosurfaces to which various coatis consequently achieved a better metalsection, and a minimization of scrap due to holes in or at the surfaceof the product.

Further where the prdouct is ultimately to be coated with an applicationof afired ceramic-type, or of a plastictype such as Teflon, it appearsthat casting in the improved molds is conducive .to a ready applicationof a sound final coating.

The general object of the present invention is. an improvement in theart of metal casting with permanent molds or die casting molds.

Another object is to provide an improved mold of the character describedwhich obviates need of frequent removal and replacement of mold cavitycoatings.

Another object is provision of a mold cavity surface resulting in alonger ultimate mold life as well as longer periods between maintenanceoperations on the cavity.

A still further object is the provision of a mold producing castings ofconsistently better and more uniform surface than obtainable bycomparable prior practice.

Other objects and advantages will appear from the following descriptionand drawings wherein:

FIGURE 1 is a fragmentary representation in section of two moldcomponents;

FIGURE 2 is a perspective view of a cast frying pan 'having a figuredsurface for the production of which this invention is particularlyadvantageous;

FIGURE 3 is a fragmentary section, similar to FIG- URE 1 through a moldfor producing the pan of FIG- URE 2, with metal cast therein, the moldconfiguration being exaggerated and certain casting layers omitted forclarity; and

FIGURE 4 shows another object, in the casting of which the presentinvention is advantageously used.

In fragmentary form, FIGURE 1 of the drawing represents two spaced moldcomponents 10' and 11 defining therebetween the cavity into which the'metal is .cast to' form the desired product. Each mold component has arespective coated portion or layer as Hip, H p; at least one of which isa porous hard chromium plating or layer, for producing that surface orsurfaces of the casting where best definition of surface configurationor best surface finish is desired, while the opposite or remainingcavity surface may be a usual coating of the prior art. q

A cast aluminum frying pan 13 is shown in FIGURE 2, having an insidebottom surface 14, which is cast between opposed mold components 16, 17(see FEGURE 3). The component 17 on its cavity surface has a -multitudeof shallow closely spaced concentric lands 18 and grooves 19, heresmoothly curved in cross'section;

which define complementary lands and grooves in the cast metal andresult in the figured bottom surface 14.

Here the lands and grooves are greatly exaggerated in size relative tothe thickness of the cast section and the portion analogous to 10p, 11pin FIGURE 1 are omitted for clarity'of the drawing. However, it is to beunderstood that with the cavity. surface of member 17 coated or platedwith porous chromium and even with the cavity surface of 16 providedwith a coating of the prior art suitable for casting such an aluminumobject, good definition of the cast pattern on the surface 14 isobtained where the grooves are on the order of 0.002 inch in depth and.003 inch in spacing. V

The cast aluminum chair base of FIGURE 4 represents another objectdifficult to obtain in uniform production by prior methods. Particularlythe concave regions at hub between the adjacent legs are subject tonon-uniformity of surface characteristics, varying in smoothness andrequiring grinding operations to get them into acceptable form forsubsequently applied finishes. The grind- 3, e ing or finishingoperationsientail considerable labor costs. Generally with conventionalmolds, there is required a fast grind with a coarse wheel, followed byanother with a less coarse Wheel, and finally a finish grind with a finegrain wheel. The multiple operations are necessitatedby the fact thatworking immediately with the fine grain wheel would take a considerabletime, cause overheating of and deterioration of the Wheel and also undueheating and deformation of the casting, which is eliminated by previoususeof a fast cutting coarse wheel, and an intermediate-wheel to removethe grain marks fromthe first operation. On the other hand, where thecorrespond ing mold surfaces have, according to the present invention, ahard porous chrome surface, only little grinding.

with a fine grained finishing wheel is required, even over extendedproduction runs, to provide a surface suitablefor plating, or otherfinish applications on the casting.

The hard porous chromium plating has been found.

quite suitable for the casting, for. example, of aluminum, zinc or.brass objects desired tohave relatively smooth finishes and also forthe reproductionof the cast objects even of mold surfaces having closelyspaced configurations.

Notonly is the invention applicable to permanent mold casting but alsoto die casting where again the die life is improved, and especially forbrass casting, where be- Generally the same ranges of plating thicknessand porosity are applicable for metals such as zinc, aluminum and brass.The upper limit in thickness of the plating is dictated as in generalplating considerations by the tendency of the layer to peel'from thecavity surface,-

a maximum chrome thickness on the order of about 0.005 inch beinggenerally safely adherent, while giving a long mold life. The etching ofa 0.005 inch plating is carried out to an average depth of about0.002-0.003 inch in the etched voids and to the extent of about 60% to80% voids in the surface area of the chromium layer. At about 60% voidsthe threshold seems to be reached of the porosity requisite for wettingby and therefore venting of the cast metal, while etching to above 80%voids leads to veining between voids, i.e., a marked joining of voids byveins or fissures penetrating to a fraction, say,

one-half to three quarters of the chromium thickness,

which results in diminishing life of the porous chrome surface.

It should be noted, however, that the thinner the .base,

plated according to this invention to obtain fine definition, forexample, a name plug in a larger mold, a relatively shallow etc, say toa depth of 0.001 inch suffices; but where a larger fiat area is plated,for example, corresponding to a pan bottom thirteen inches in diameter,a deeper etch, say about 0.002 inch, is indicated.

I claim:

'1.,A non-porous mold defining a metal cavity adapted to receive amolten metal to be cast comprising a mold coating of hard chromiumadhering to the mold cavity in physical contact with the metal beingcast and having a surface porosity defined by a network of voidsextending uniformly over about 60% of the mold coating area and to anaverage depth of at least 0.002 inch whereby entrained gases in themetal are vented through the coating.

2. A non-porousmoldas set forth in claim 1 wherein said surface porosityis formed by electroetching the chromium coating.

3. A non-porous mold as set forth in claim 2 wherein thethickness of thechromium coating is'approximately 0.005 inches.

4. A non-porousmold as set forth in claim 3 wherein the network of voidsextends over about 60% to of the coating area and to anaverage depth ofbetween 0.002 and 0.003 inches.

5. A non-porous mold defining a mold cavity adapted to receive a moltenmetal to be cast comprising an electro-deposited mold coating of hardchromium adhering to the mold cavity andin physical contact with themetal being cast and having an electroetched surface porosity defined bya network of voids extending uniformly over about 60% of the moldcoating area and to an average depth of at least 0.002 inches wherebyentrained gases in the molten metal are vented through the coating.

6. The method of making a self-venting, non-porous mold having a moldcavity adapted to receive a molten metal to be cast therein comprisingthe steps of: electroplating a portion of the cavity with a hardchromium layer having a thickness of approximately 0.005 inches.

and anodically etching the chromium layer for a period sufiicient toproduce a surface porosity therein defined by a network of voidsextending uniformly over about 60% of the chromium layer and to anaverage depth of at least 0.002 inches whereby entrained gases. in themetal are vented through the chromium plate.

References Cited by the Examiner,

UNITED STATES PATENTS 1,678,117 7/28 Homberg 106-3 8;27 1,794,536 3/3 1Quinn 117--5.3 1,809,872 -5/27 Soderberg 106-3827 2,031,568 *2/36Lemmerman 22-2165 2,217,802 10/40 Koehring 10638.27 2,363,337 11/44Kelly 106-3827 2,479,364 8/49 Jocelyn 22216.5

OTHER REFERENCES Metal Handbook, 1948 Ed., Porous Chromium, page 719.

MICHAEL V. BRINDISI, Primary Examiner.

MARCUS U. LYONS, Examiner.

1. A NON-POROUS MOLD DEFINING A METAL CAVITY ADAPTED TO RECEIVE A MOLTENMETAL TO BE CAST COMPRISING A MOLD COATING A HARD CHROMIUM ADHERING TOTHE MOLD CAVITY IN PHYSICAL CONTACT WITH THE METAL BEING CAST AND HAVINGA SURFACE POROSITY DEFINED BY A NETWORK OF VOIDS EXTENDING UNIFORMLYOVER ABOUT 60% OF THE MOLD COATING AREA AND TO AN AVERAGE DEPTH OF ATLEAST 0.002 INCH WHEREBY ENTRAINED GASES IN THE METAL ARE VENTED THROUGHTHE COATING.